Series interlock system with integrated ability to identify breached locations

Abstract

A system is provided for implementing a series interlock loop. An example of the interlock system includes a series interlock loop, a data table, and a control module. The series interlock loop has an overall electrical characteristic. The series interlock loop includes first and second safety interlocks electrically coupled in series. Each interlock includes a switch coupled in parallel with an impedance value. The data table is configured to store values corresponding to the impedance values. The control module is communicatively coupled to the data table and configured to receive an indication of the overall electrical characteristic and to compare the overall electrical characteristic to the values in the data table to thereby identify an open one of the first and second safety interlocks.

1. An interlock system comprising:
 a series interlock loop having an overall electrical characteristic comprising:
 a first safety interlock comprising a first switch coupled in parallel with a first impedance value; 
 a second safety interlock electrically coupled in series with the first safety interlock, the second safety interlock comprising a second switch coupled in parallel with a second impedance value; and 
 
 a control module communicatively coupled to a data table with values, and configured to receive an indication of the overall electrical characteristic and to compare the overall electrical characteristic to the values in the data table to thereby identify an open one of the first and second safety interlocks. 
 
     
     
       2. An interlock system according to  claim 1  the control module comprising a source, a resistor, and an analog to digital converter, wherein the resistor is electrically coupled in series with the series interlock loop, and wherein the analog to digital converter is electrically coupled to the series interlock loop to measure the overall electrical characteristic and to convert the overall electrical characteristic to a digital value. 
     
     
       3. An interlock system according to  claim 1  wherein the data table correlates a first overall electrical characteristic to a first state of the series interlock loop, a second overall electrical characteristic to a second state of the series interlock loop, and a third overall electrical characteristic to a third state of the series interlock loop. 
     
     
       4. An interlock system according to  claim 3  wherein the first state corresponds to a single open position in the series interlock loop at the first safety interlock, the second state corresponds to a single open position in the series interlock loop at the second safety interlock, and the third state corresponds to an open position of both the first safety interlock and the second safety interlock. 
     
     
       5. An interlock system according to  claim 1  wherein the control module is configured to obtain the overall electrical characteristic and to compare the overall electrical characteristic to the values stored in the data table to thereby identify a breach in either of the first and second safety interlocks. 
     
     
       6. An interlock system according to  claim 1  wherein the series interlock loop further comprises a third safety interlock electrically coupled in series with the first safety interlock and the second safety interlock, the third safety interlock comprising a third switch coupled in parallel with a third impedance value, wherein the first impedance value, the second impedance value, and the third impedance value have different values numerically related by a geometric progression. 
     
     
       7. A system to determine locations of breached interlocks in a series interlock loop comprising:
 a first safety interlock at a first location in the series interlock loop comprising a first open position and a first open interlock impedance value corresponding to the first open position; 
 a second safety interlock at a second location in the series interlock loop electrically coupled in series with the first safety interlock, the second safety interlock comprising a second open position and a second open interlock impedance value corresponding to the second open position; and 
 a sensor configured to measure an overall electrical characteristic of the series interlock loop, wherein the overall electrical characteristic has a first overall impedance value corresponding to the first open interlock impedance value when only the first safety interlock is breached, and a second overall impedance value corresponding to the second open interlock impedance value when only the second safety interlock is breached, wherein the first overall impedance value is different from the second overall impedance value. 
 
     
     
       8. A system according to  claim 7  further comprising a controller communicatively coupled to the sensor, the controller configured to change a condition in a device based on the overall electrical characteristic. 
     
     
       9. A system according to  claim 7  wherein the second open interlock impedance value is greater than the first open interlock impedance value. 
     
     
       10. A system according to  claim 7  wherein the first safety interlock further comprises a first switch coupled in series with a first resistor with a first resistive value, and wherein the first open interlock impedance value corresponds to the first resistive value. 
     
     
       11. A system according to  claim 10  wherein the first safety interlock further comprises a first closed interlock impedance value that corresponds to a short circuit across the first resistive value when the first switch is closed. 
     
     
       12. A system according to  claim 7  wherein the overall electrical characteristic of the series interlock loop is substantially equal to a sum of the first open interlock impedance value and the second open interlock impedance value when the series interlock loop is breached at the first location and at the second location. 
     
     
       13. A system according to  claim 7  wherein the first open interlock impedance value is a first resistive value and wherein the second open interlock impedance value is a second resistive value twice the value of the first resistive value. 
     
     
       14. A system according to  claim 7  further comprising a third safety interlock at a third location in the series interlock loop electrically coupled in series with the first and second safety interlocks, the third safety interlock comprising a third open position and a third open interlock impedance value corresponding to the third open position, wherein the first open interlock impedance value, the second open interlock impedance value and the third open interlock impedance value have different values numerically related by a geometric progression. 
     
     
       15. A method of implementing a safety interlock system, wherein the safety interlock system comprises a series interlock loop with multiple interlocks each comprising a unique impedance value, a data table storing values corresponding to unique states of the series interlock loop, and an overall electrical characteristic of the series interlock loop, the method comprising:
 obtaining a numerical value representing the overall electrical characteristic of the series interlock loop; 
 identifying a breached interlock by comparing the numerical value to the values stored in the data table; and 
 providing an output indicating the breached interlock. 
 
     
     
       16. A method according to  claim 15  further comprising sensing the overall electrical characteristic. 
     
     
       17. A method according to  claim 15  further comprising detecting multiple breaches in the series interlock loop. 
     
     
       18. A method according to  claim 15  further comprising obtaining an operating condition. 
     
     
       19. A method according to  claim 18  further comprising identifying a shutdown condition based on the numerical value and the operating condition. 
     
     
       20. A method according to  claim 18  wherein the operating condition includes operating conditions of a motor vehicle with a high voltage electrical system.